1. Field of the Invention
The present invention relates to wire clamps of the type used on semiconductor wire bonding machines. More particularly, the present invention relates to balanced low mass wire clamps that will withstand very high gravitational forces without a change in clamping forces.
2. Description of the Prior Art
Wire clamps for wire bonders are classified in U.S. Class 228, subclass 4.5 and in International Class B23K subclasses 37/00 and 31/02. It is known by wire clamp designers that wire clamps must be capable of moving from an open to a closed position and vice versa rapidly on command. Some bonding machines are capable of making up to ten wire interconnections per second. Each bonded wire requires opening and closing the wire clamp at least four times or forty position changes per second. This rapid movement requires rapid acceleration and deceleration of moving parts to effect the desired change of position of the jaws of the wire clamps and desired clamping forces.
In a closed position the jaws of the wire clamp must exert a low predetermined clamping force designed to hold a gold wire without causing deformation. The gravitation forces exerted on the parts of a wire clamp often exceed 30 g's. Every pivotable and moveable part has a center of gravity representative of the center of mass of the movable part which is accelerating and decelerating at 30 g's (32.4 feet per second.sup.2). This acceleration is translated into forces applied to the jaws of the wire clamp. Heretofore, wire clamp for wire bonders were designed to generate symmetrical counter-balanced forces to prevent the acceleration and deceleration forces from generating harmful forces at the jaws of a wire clamp. Examples of such balanced force wire clamp are shown and described in U.S. Pat. Nos. 4,653,681 and 5,277,355, assigned to the same assignee as the present invention, and are incorporated by reference herein.
It is also known that the unbalanced forces of acceleration and deceleration may be reduced by reducing the size and mass of the moving parts in a wire clamp. Thus, the elements which comprise the parts of a wire clamp can be reduced to further reduce unwanted forces at the wire clamp jaws.
It would be desirable to provide a universal wire clamp assembly that embodies low mass pivotable levers with a low mass actuator that can be symmetrically balanced against undesirable inertia forces.